There is compelling evidence that different regions of the auditory cortex are specialized for processing 'what' a sound is and 'where' in space it is coming from. The long term goal of this project is to understand the neural and anatomical basis for this specialization. Aim 1 addresses the neural basis for specialization. The manner in which specialization for sound pattern and sound location arises from single unit activity is unknown. This question will be investigated from the vantage point of two cues for sound pattern and location -- amplitude modulation (AM) and interaural time differences (ITDs), respectively. We will record single unit responses to AM and ITD in three areas of auditory cortex in unanaesthetized rabbits: the primary auditory cortex (A1), the dorsal anterior area (DA), and the ventral area (V). For each neuron, we will: i) determine whether it is ITD- sensitive, or AM-sensitive, or both ii) measure the 'quality' with which it encodes ITD or AM, and iii) measure the 'invariance' with which it encodes ITD when AM is varied, and vice versa. In this way, Aim 1 will determine whether ITD and AM sensitivity are represented preferentially in areas V and DA of the rabbit auditory cortex, respectively. Aim 2 addresses the anatomical basis for specialization. Nonprimary auditory areas receive many intracortical connections from A1, yet they are more specialized than A1. We hypothesize that this specialization is engendered by separate sets of connections from within A1 to each of the nonprimary areas. We will investigate this by placing different anatomical tracers at frequency matched sites of the nonprimary auditory cortical areas, DA and V, of rabbits. The distribution of labeled material within A1 will be analyzed and, in this way, Aim 2 will determine whether connections between A1 and DA ore organized differently than the connections between A1 and V. The two main tasks of the auditory cortex are to determine 'what' a sound is and 'where' it is coming from. This project will determine how neurons in different areas of the auditory cortex respond to 'what' and 'where' signals and how their connections enable them to do this. This information will be essential for designing hearing prosthetic systems that are implanted in the cortex. [unreadable] [unreadable] [unreadable]